Process for cracking mineral oils



Patented May 23, 1939 PATENT OFFICE PROCESS FOR CRACKING MINERAL OILS Hugh" M. Corrough, Tulsa, Okla., assignor to Power Patents Company, Hillside, N. J., a corporation of Maine Application November 2, 1934, Serial No, 751,139

4 Claims.

This invention relates to a process for cracking mineral oils and more particularly to such a process for making high octane gasoline and in which the residue of the cracking operation is coked to produce a marketable fuel.

A number of cracking processes have been developed and put into use which involve the coking of the residue by collecting it in an enlarged chamber. The coking units employing such proc- ;esses however have been operated at transfer line temperatures suitable for therproduction of a coke that could be easily removed from the chamber. The transfer line temperatures in such units have usually been relatively low so that it ;was practically impossible to produce a high anti-knock gasoline and atthe same time produce a coke which could be easily removed from the coke chambers.

The primary objectsof the present invention 018.16 therefore to provide an efiicient cracking operation for the cracking of heavy hydrocarbon oils to produce gasoline and coke in which the cracking temperature and coke formation are independently controlled in such a way as to defi- ,;,-.;nitely and positively produce a hard-firm, mar:

" ketable coke and at the same time produce a high octane gasoline. I

In accordance with these and other objects of the invention, the improved process comprises the steps of heating the oil to be cracked, to the desired high cracking temperature in a pipe, still furnace and maintaining the temperature of the oil for a suflicient period of time to cause the desired conversion of the oil to gasoline, thereafter discharging the highly heated cracked products into the upper portion of an enlarged cokecollecting chamber in which the unvaporized oil constituents are permitted to collect and. coke, introducing into the enlarged chamber at ap- ,-proximately the coke level therein, a small pro- 1 portion of a heavy hydrocarbon oil to control the coking operation, removing the vapors from the enlarged chamber, and subjecting them to fractionation for the separation of the desired gasoline product. v J Further objects and advantages of the improved process of the invention will be apparent from the following detailed description thereof I taken in connection with the accompanying 5D drawing in which the figure is a. diagrammatic flow sheet showing an apparatus adapted'to carry out the process of the invention.

Referring to the drawing, the oil to be cracked which is preferably a topped crude, fuel oil or gas oil stock is introduced into the system through a line 2 and forced by means of a pump 4 through valved lines 6 and 8 into the upper portion of a fractionating tower H). The charging stock is passed downwardly through the tower Ill in a preheating coil I2 and discharged onto the lowermost tray near the bottom of the tower. The charging stock and reflux condensate is collected in the base of the tower and conducted therefrom through a line l4 and forced under high pressure by means of a pump l6 through 10 heating and cracking tubes I8 mounted in a pipe still furnace 20.

, The oil in passing through the pipe still furnace is heated up to the desired high cracking temperature of approximately 915 F. and there- 15 after malntained at that temperature or slightly higher (980 to 1000 F.) in the upper tubes of the furnace. "I'hehighly heated and cracked products are discharged from the upper tubes of the pipe still furnace and conducted through a transfer line 22 into the upper part of coking chamber 24. In this chamber the vaporized and unvaporized oil constituents separate, the latter collecting in the chamber and being converted to coke by their own heat content, while the vapors are conducted through a vapor line 26 into the lower part of fractionating tower II].

In bringing the apparatus on stream the oil discharged into the chamber 24 is withdrawn through a valved line 28 into the lower part of 30 tower l0 so that it is recirculated through the pipe still furnace. This operation is continued until the desired operating temperature and pressure is attained in the apparatus, after which the valve in line 28 is closed.

The oil residue continuously depositing in the coke chamber 24, is gradually converted into a solid coke mass. In accordance with the features of the present invention the coking operation in the chamber 24 is controlled independent of the transfer line temperature by the introduction of a small proportion of heavy oil into the chamber at a point slightly above the coke level therein. This is accomplished by introducing from 2% to 20% of the heavy oil charging 4 stock from the valved line 6 through a valved line 30, and conducting it through one 'of the valved branch lines 32 into the chamber 24 at the appropriate level, The proportion of added oil will depend on its temperature and the transfer line temperature. The proper level for introducing the oil directly into the chamber 24 may be ascertained by the use of the valved sample lines 34.

For example, the experienced operator in following the progress of his cracking unit will know approximately the height of the coke in the chamber at any given time. He will then at frequent intervals open two or more adjacent lines 34 until he finds one that will not draw liquid, adjacent to one that does draw liquid. He then knows that the oil being introduced in the chamber should be introduced through the branch line 32 which is adjacent the line 34 which will not draw liquid. In carrying out this operation, it hasbeen' found that satisfactory results are obtainable in many cases by using from 3% to 5% of the cold heavy charging stock introduced by the pump 4. The proper quantity may be accurately metered by means of the meter in line 30.

The oil introduced into the coking chamber through any of the lines 32 is preferably a heavy oil such as fuel oil, topped crude "or other oil' A (hot) concentrator residue from. a,

' 24 at approximately the coke level is not definite ly understood,but repeated comparisons of the coke formed without this oil, with the coke formed when the oil is introduced, shows that a decidedly superior coke product is obtained in the one instance, while a scarcely marketable coke is obtained in the other. It may be that the highly polymerized oil constituents collecting in the chamber 24 from transfer line 22 (in the absence of the fresh heavy oil) tend tocoloe out too quickly and thereby produce a porous fragile coke. Regardless of the specific reactions taking place in the operation a few per cent of such added oil based on the charging stock, completely changes the quality of the coke resulting from the operation as well as the ease of its removal from the chamber. I

The process of the present invention is particularly adapted for the cracking of heavy oils such as fuel oil stocks, topped crudes and heavy gas oils which are completely converted into gasoline and coke. desired outlet temperature which is particularly adapted for producing a high octane gasoline,

without regard to the character of thecoke whichmight be produced in the chamber 24 as the result of such high temperature operation, because the coking of the oil residue in the chamber 24 is independently controlled by the introduction of regulated quantities of heavy oil at the coke level as it rises in the chamber.

The tower I is preferably operated at substantially the same pressure as the chamber 24 which may rangefrom a pressure of 150 pounds per square inch to 300 pounds per square inch. This tower is also operated so as to deliver a vapor fraction which comprises substantially end point gasoline or pressure distillate. These vapors are conducted from the top of the tower through a vapor line 40, condensed in condenser 42 and the resulting condensate conducted into a receiver 44. This receiver is preferably maintained under a high pressure which is substan tially that of chamber 24, so that dry gas may be vented through a valved line 46. The pressure distillate is discharged from receiver 44- through I a valved line and any-part of this pressure The process may be operated 'at the distillate may be used for controlling the fractionating operation in tower Ill by conducting it through line 50 in which is mounted a thermostatically controlled pump 52.

The cracking unit described above may be operated substantially continuously by providing alternative chambers 24 so that one may be cut out of the circuit and cleaned while the other is being filled with coke. A heat exchanger may be mounted in the vapor line 26 'for preheating the charging stock or oil introduced through lines 30 and 36, or a relatively cool clean oil or water mayfi'be introduced into this line to quickly cool the vapors discharged from the chamber 24. Various other modifications of the apparatus and process'may be'made without departing from the spirit and scope of the invention defined herein. It is to be understood that the invention is not limited as to detail except as so limited by th claims.

Having'thus described the invention in its preferred form; what is claimed as new is:

1. In the process of cracking heavy hydrocarbon oils for'theproduction of coke and gasoline in which a heavy hydrocarbon oil is conducted in a confined stream of restricted cross section through a heating zone wherein the oil is heated to a cracking temperature and cracked to produ'ce a substantial proportion of gasoline, and in which the resulting heated cracked products are discharged at approximately the temperature at which they leave the heating zone into the upper portion of an enlarged coking chamber wherein vapors are permitted to separate from unvaporized residual oil and" where coke formation from substantially the entire separated residual oilis permitted to take place, the improvement which comprises removing separated vapors from the upper part of the coking chamber andfractionating them in a tower to separate the gasoline constituents as vapors, passing the heavy hydrocarbon oil charging stock for the process downwardly through said tower in indinot heat exchange with vapors,- passing the resulting preheated charging stockand reflux condensate produced from said vapors in said tower to said heating zone to be heated and cracked therein, heatingthe oil stream in said heating zone to a temperature of from 915 to 1000 F. which is sufficiently high'to produce a gasoline of'substantially higher octane value than that normally produced in a cracking and coking operation of the type referred to, which temperature is too' high for the production of a readily removable hard firm marketable coke in said chamber from the separated'residual oil, maintaining the separated residual oil at a coking temperature in said chamber by its contained heat, controlling the'coking of the residual oil in said chamber to obviate the adverse effect of the high temperature to which the residual oil products'were heatedin the heating zone by introducing into said chamber at approximately the-coke level as'it rises therein a quantity of a relatively cool heavy residual hydrocarbon oil equivalent to approximately of the charging oil for the process to. promote the formation of a'hard firm marketable coke from the unvaporized residual oil separated out in said chamber and the introduced residual oil.

2. In the process of cracking heavy hydrocarbon oils for the production of coke and gasoline in which a heavy hydrocarbon oil is conducted in'a confinedstream of restricted cross section througlra heating zone wherein the oil is heated to a cracking temperature and cracked to produce a substantial proportion of gasoline, and in which the resulting heated cracked products are discharged at approximately the temperature at which they leave the heating zone into the upper portion of an enlarged coking chamber wherein vapors are permitted to separate from unvaporized residual oil and where coke formation from substantially the entire separated residual oil is permitted to take place, the improvement which comprises heating the oil stream in said heating zone to a temperature sufiiciently high to produce a gasoline of substantially higher octane value than that normally produced in a cracking and coking operation of the type referred to, which temperature is too high for the production of a readily removable hard firm marketable coke in said chamberfrom the separated residual oil, removing the separated vapors from the upper part of the enlarged chamber and separating out the gasoline therefrom, maintaining the separated residual oil at a coking temperature in said chamber by its contained heat, controlling the coking of the residual oil in said chamber to obviate the adverse effect of the high temperature to which the residual oil products were heated in the heating zone by introducing into said chamber at approximately the coke level as it rises in said chamber a small proportion of a relativel ool heavy residual hydrocarbon oil based on the quantity of charging stock, to promote the formation of a firmi hard marketable coke from the unvaporized residual oil separated out in said chamber and the introduced residual oil.

3. In the process of cracking heavy hydrocarbon oils for the production of coke and gasoline in which a heavy hydrocarbon oil is conducted in a confined stream of restricted cross section through a heating zone wherein the oil is heated to a cracking temperature and cracked to produce a substantial proportion of gasoline, and in which the resulting heated cracked products are discharged at approximately the temperature at which they leave the heating zone into the upper portion of an enlarged coking chamber wherein vapors are permitted to separate from unvaporized residual oil and where coke formation from substantially the entire separated residual oil is permitted to take place, the improvement which comprises heating the oil stream in said heating zone to a temperature of at least 915 F. which is sufficiently high to produce a gasoline of high octane value but too high for the production of a readily removable coke from the separated residual oil in said chamber, removing the separated vapors from the upper part of the enlarged coking chamber and separating out the gasoline therefrom, maintaining the separated residual oil at a coking temperature in said chamber to efiect the coking of the residual oil and accumulate the coke in the chamber, determining the approximate position of the coke level as it rises in the chamber during the continuance of the cracking and coking operation, and introducing a heavy residual oil directly onto the coke body as it rises in said chamber, the quantity of such introduced oil being approximately 5% of the charging stock for the cracking process, whereby the unvaporized residual oil separated out in said chamber and the introduced residual oil is coked into a firm marketable coke which is readily removable from the chamber.

4. In the process of cracking heavy hydrocarbon oil for the production of coke and gasoline in which a heavy hydrocarbon oil is conducted in a confined stream of restricted cross section through a heating zone in which the oil is heated to a cracking temperature and cracked to produce a substantial proportion of gasoline, and in which the resulting highly heated cracked products are discharged at approximately the temperature at which they leave the heating zone into the upper part of an enlarged coking chamber where vapor separation is efiected and coke formation from substantially all of the unvaporized residue occurs solely from the contained heat thereof, the improvement which comprises removing the separated vapors from the upper part of the coking chamber, regulating the cracking temperature to which the confined stream of oil is subjected and maintaining a temperature of at least 915 F. which is sulficiently high and the time of heating at the cracking temperature sufliciently long to produce a high octane gasoline, maintaining the separated unvaporized residue in said chamber at a coking temperature by its contained heat, and independently controlling the quality of the coke formed in said coking chamber to improve the same over that which would normally be formed in said chamber from said residue to produce a hard firm marketable coke by introducing directly onto the coke bed as it rises in said chamber a regulated relatively small proportion of heavy hydrocarbon oil equivalent to approximately 5% of the charging stock for the process.

HUGH M. CORROUGH. 

